Lossy WebP encoder: default to effort 2

Effort 3 and up add the full rate-distortion search of the intra 4x4
modes: on a 1920x1080 photo at quality 75, effort 2 takes ~245 ms for
101.6 kB (38.87 dB), effort 4 ~905 ms for 96.6 kB (39.32 dB). The
default becomes 2 for images and animations; effort 4 still encodes like
cwebp's default.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Lfv41PqHEGbU7SLg5onpG1

Author: matmen

CHANGELOG.md

@@ -10,6 +10,9 @@
 
 ### Improvements
 
+- Lossy WebP encoding defaults to `effort: 2` instead of 4: about a quarter of the time (about 250 ms instead of
+  900 ms for a 1920x1080 photo) for files about 5% larger at a slightly lower quality (about 0.5 dB PSNR).
+  `effort: 4` encodes like cwebp's default as before.
 - AVIF encoding also tries splitting blocks into halves (horizontal or vertical, from 64x64 to 16x16) where the whole
   block and its quarters cost about the same: files about 2% smaller at the default effort, encoding about 20% slower.
 - AVIF encoding with `effort: 2` also chooses smaller transforms within blocks (transform depth): files about 1% smaller

src/animation.ts

@@ -62,7 +62,7 @@ export interface WebPAnimationEncodeOptions extends AnimationEncodeOptions {
      * frames are lossless
      */
     quality?: number;
-    /** How much effort lossy frames take (0-6), see {@link WebPEncodeOptions.effort}. Default: `4` */
+    /** How much effort lossy frames take (0-6), see {@link WebPEncodeOptions.effort}. Default: `2` */
     effort?: number;
 }
 
@@ -287,7 +287,7 @@ export class Animation extends Array<Frame> {
      * shows the same animation, but doesn't necessarily decode to the same frames
      * @param options See {@link WebPAnimationEncodeOptions}
      */
-    async encodeWebP({ metadata = {}, optimize = true, quality, effort = 4 }: WebPAnimationEncodeOptions = {}): Promise<Uint8Array> {
+    async encodeWebP({ metadata = {}, optimize = true, quality, effort = 2 }: WebPAnimationEncodeOptions = {}): Promise<Uint8Array> {
         this.__validate__();
         if (!this.length) throw new Error('An animation needs at least one frame');
         if (quality !== undefined) {

src/image.ts

@@ -106,13 +106,13 @@ export interface JPEGEncodeOptions {
 export interface WebPEncodeOptions {
     /**
      * Lossy compression (0-100, like libwebp's quality: 75 is its default): the image is encoded like cwebp encodes it
-     * with its default settings, much smaller than lossless. Without it the image is encoded losslessly
+     * (with `-m` set to the effort), much smaller than lossless. Without it the image is encoded losslessly
      */
     quality?: number;
     /**
      * How much effort lossy compression takes (0-6, libwebp's method): higher is smaller but slower. 0-2 pick the
      * predictions by how close they are, 3 and up also by how many bits they take, 5 and 6 also optimize the
-     * quantized values. Default: `4` (like cwebp)
+     * quantized values. Default: `2`: about a quarter of the time of 4 (cwebp's default) for files about 5% larger
      */
     effort?: number;
     /** Metadata to include, see {@link Metadata} */
@@ -2045,7 +2045,7 @@ export class Image {
      * quality
      * @param options See {@link WebPEncodeOptions}
      */
-    async encodeWebP({ quality, effort = 4, metadata = {} }: WebPEncodeOptions = {}): Promise<Uint8Array> {
+    async encodeWebP({ quality, effort = 2, metadata = {} }: WebPEncodeOptions = {}): Promise<Uint8Array> {
         const exif = exifData(resolveMetadata(metadata));
         if (quality === undefined) return webp.encode(this.__bytes__(), this.width, this.height, exif);
         const q = finite(quality, 'quality');